Gypsy Moth

Common Name: Gypsy Moth
Latin Name:  Lymantria dispar
Order: Lepidoptera

Family: Lymantriidae

Main Host(s)Most species of Oak (Quercus), as well as Apple (Malus), Basswood (Tilia), Willow (Salix), and many other species of trees and shrubs. It is estimated that Gypsy Moth will feed upon over 500 species of trees shrubs and vines.

Life Cycle

The European Gypsy Moth is found throughout Europe and in numerous locations in North America. Accidentally introduced to North America in 1869, Gypsy Moth has spread across eastern North America from the Carolinas north to the Great Lakes and west to the Mississippi River. Periodically, isolated introductions have occurred in western North America.

Eggs are laid in large masses by the female moth in mid summer. As the eggs are expelled, the female sheds abdominal hairs building a protective buff coloured patch or mass of eggs about 1-2 inches in length (2.5-5.0 cm) and 0.5 to 1.0 inches (1.2-2.5 cm) in width. The eggs are laid in masses containing 200-1000 eggs, usually in protected or sheltered areas.  They may be found on the lower trunk and the underside of lower tree limbs, on nearby rocks, or even on manmade structures.

The embryo develops to become a small larva within the egg which enters diapause for the overwintering stage of its lifecycle. The following spring, the larvae continue to develop and hatch. After hatching, the small first instar larvae stay close to the egg mass and within a few days begin to migrate into the upper canopy. Spinning long silken threads, the tiny larvae are readily dispersed by spring breezes throughout the surrounding forest.

The larvae move into the canopy to feed, but return to the lower areas when the daytime temperatures begin to climb. However, as the forest canopy begins to leaf out and the larvae mature, they remain in the canopy throughout the day and night, feeding voraciously. The earliest signs of defoliation will be small holes in the leaves, giving a gunshot-like appearance. As defoliation intensifies, all foliage will be consumed, and in extreme cases, the larvae will cross branches or move along the ground to find other sources of foliage.

The larvae have several stages, or instars, (five for males, six for females) with the appearance of distinctive dorsal patterns, pairs of blue and red dots, or tubercules, prominently visible in the latter stages.

The larvae pupate in a small reddish brown coloured cocoon for 7-14 days and emerge as an adult moth; moths live for about two weeks. The female moth (1.5 inches, 4.0 cm) is larger than the male and is easily recognized by white wings and distinctive black wavy V-shaped markings. She does not fly, and remains in the general area in which she emerged from her pupal case. The smaller male moth is dark brown in color with black wavy V wing markings. The males usually emerge from the pupae earlier than the females and fly about searching for females.

Impact & Damage

Gypsy Moth Egg StageEgg Stage
Source: PA DCNR

Gypsy Moth Larval StageLarval Stage
Source: John H. Ghent, USDA/FS, Bugwood.org

John H. Ghent, USDA/FS, Bugwood.orgPupal Stage
Source: John H. Ghent, USDA/FS, Bugwood.org

Gypsy Moth Adult StageAdult Stage
Source: John H. Ghent, USDA/FS, Bugwood.org

Gypsy Moth DefoliationDefoliation

The European Gypsy Moth, commonly referred to as Gypsy Moth in North America, is found throughout the oak forests of Europe and Eurasia as well as the across the eastern sector of the North American continent.  A voracious defoliator, the Gypsy Moth has caused extensive damage to the oak forests of the Northeast and the Midwest US. Significant levels of oak morbidity and mortality have been recorded in areas repeatedly defoliated by the Gypsy Moth.

Additionally many residential areas of the eastern USA are located within suitable host range for the Gypsy Moth. Some people are allergic to the urticating hairs of the larvae and the defoliation of residential hardwood trees along with the associated debris and frass can prove stressful to property owners.

Periodically the Gypsy Moth has been introduced into other areas of North America, usually west of those areas considered as generally infested. These incursions usually trigger government control and eradication efforts to help ensure that this invasive pest is limited to its current range.

Extensive defoliation can cause significant impacts on individual tree and forest health. As with many defoliators, even one year of defoliation can cause a reduction in growth and yield. Several years of defoliation can cause significant tree and stand mortality.

Reference & Sources:

British Columbia Ministry of Forests
Forestry Images
Pennsylvania Department of Conservation; Natural Resources
USDA Forest Service

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